1. Field of the Invention
The present invention is directed to combination locks having protection against manipulation.
2. Description of the Prior Art
The manipulation of combination locks is an art which has developed in step with the development of devices fitted to these locks with the object of preventing this manipulation. The term "manipulation" is used in connection with combination locks to mean the continued operation of the dial of the lock through successive steps in alternately opposite directions on a trial basis, as a result of which the manipulator gradually informs himself of the correct combination of the lock and can eventually open it. At each stage in the development of protective devices to prevent manipulation, the manipulator is foiled until he develops techniques or equipment which use some hitherto untried feature for determining the relative location of the probe or "fence" as it is commonly called and the gates in the respective wheels of the lock. One common feature of all manipulation techniques is that many trial diallings are required and the present invention is based on a practical utilisation of this feature to achieve the desired protection.